1. Field of the Invention
The present invention relates to a driving circuit for a stepping motor.
2. Description of the Related Art
An optical disc apparatus includes an optical pickup configured to emit a laser beam to an optical disc and receives the laser beam reflected by the optical disc. A stepping motor is used to move the optical pickup in the radial direction of the optical disc.
In the optical disc apparatus, a position in the radial direction (hereinafter, referred to as “radial position”) of the optical pickup needs to be determined when the power of the optical disc apparatus is turned on. Therefore, when the power is turned on, the radial position of the optical pickup is determined by moving the optical pickup to the end of the range of the movement of the optical pickup in the radial direction of the optical disc (generally an innermost or an outermost circumferential portion).
For example, Japanese Laid-Open Patent Publication No. 2009-65806 discloses a stepping motor driving apparatus configured to detect an induced voltage generated in a driving coil of the stepping motor and determine whether a rotor of the stepping motor is stopped, based on the detected induced voltage. As such, whether the rotor is stopped is determined based on the induced voltage, thereby being able to detect the state where the optical pickup reaches the innermost or the outermost circumferential part (hereinafter, referred to as “collision state”), without using any position detecting means such as an optical sensor or a contact switch. The radial position of the optical pickup is able to be determined as well as it is possible to prevent wearing away of portions such as a screw shaft that is rotated by the stepping motor and the gear portion that meshes with the screw shaft, by stopping the supply of a driving current to the driving coil after the detection of the collision state.
Whereas, for example, Japanese Laid-Open Patent Publication No. 2000-173203 discloses a pickup moving apparatus having a releasing unit, configured to release the meshing of the screw shaft with the gear portion, provided at each of the innermost and the outermost positions of the screw shaft. As such, it is possible to prevent the wearing away in the central portion of the gear portion without using any position detecting means by releasing the meshing of the screw shaft with the gear portion at the ends of the screw shaft at which the optical pickup is in the collision state, and causing the screw shaft to rotate free. It is possible to move the optical pickup in the opposite direction by reversely rotating the screw shaft by biasing the optical pickup, which has been moved to the end of the screw shaft, such that the gear portion meshes with the screw shaft.
The stepping motor driving apparatus of the above Japanese Laid-Open Patent Publication No. 2009-65806 is configured to detect the collision state based on the result of the determination on whether the rotor is stopped. However, the pickup moving apparatus of the above Japanese Laid-Open Patent Publication No. 2000-173203 may not be able to detect the collision state when the stepping motor driving apparatus of the above Japanese Laid-Open Patent Publication No. 2009-65806 is applied thereto because the screw shaft rotates free and the rotor does not stop in the collision state.
Therefore, different methods of determining the presence of the collision state need to be used depending on whether the rotor stops or rotates in the collision state.